The present invention relates in general to structural members and, more specifically, to light-weight, weather-proof structural members adapted for constructing lawn furniture, outdoor gym equipment and the like.
Structural members of light-weight plastic material are known for use in the construction of lawn furniture as exemplified by U.S. Pat. No. 4,674,799. In producing such lawn furniture, it is desirable to select materials which are impervious to the weather such that the furniture will not rot, rust, corrode, etc., which are readily available, and which are suitable for mass production techniques. It is further desirable to construct the lawn furniture of materials such that they may be easily moved and stored. Despite the desire to make the furniture light-weight, it is still necessary to make the furniture as rugged and sturdy as possible, hence, the use of the structural member disclosed in the aforementioned patent so as to balance the trade-offs between competing design engineering criteria.
The known structural member includes a rigid outer plastic member having two spaced-apart web members which divide the hollow interior into three longitudinally-extending chambers. To provide mechanical strength to the outer plastic member, a hollow, cylindrical metal tube is inserted into the middle chamber. The resulting structural member now possesses the requisite corrosion resistance, light-weight characteristics and sufficient mechanical strength to be used in constructing frames for lawn furniture and the like.
Although the known structural member has found utility in the construction of lawn furniture, gym equipment and the like, it is desirable to fabricate such a structural member from a single material, i.e., light-weight plastic, employing a simple extrusion process. Specifically, it is desirable to eliminate the need of incorporating a metal tube within an otherwise all-plastic structural member to provide mechanical strength. In addition, the necessity of securing one structural member to another has required the use of special plug inserts positioned within a chamber to receive a fastener such as a bolt or the like. Such a plug insert, typically of plastic material including a threaded metal insert, is fit into one chamber at the free end of each structural member that requires attaching to another such member or the like. Although the known plug is secured within the chamber by a single external screw, such plug insert can become loose during use of the lawn furniture over its useful life, thereby rendering the lawn furniture unstable at the locations of the structural member's interconnections.